The objective of this project is to investigate extracellular matrix-cell interactions employing an experimental system of matrix-induced endochondral bone differentiation. This experimental model further affords a method to undertake systematic studies on the biochemistry and physiology of endochondral bone formation. Subjects currently under investigation are: (1) the mechanism of action of matrix components in bone differentiation; (2) role of fibronectin in collagenous matrix-mesenchymal cell interaction; (3) biochemical mechanisms involved during vascular invasion of cartilage; (4) developmental appearance of vitamin-K dependent bone gamma-carboxyglutamic acid containing protein; (5) changes in polyamines and RNA synthesis during matrix-induced cartilage, bone and bone marrow development; (6) changes in intracellular enzymes of collagen biosynthesis during endochondral bone development; (7) local influence of somatostatin of endochondral bone development; and (8) activity and distribution of lysosomal enzymes during bone and bone marrow development.